Engines may include crankcase ventilation systems to vent gases out of the crankcase and into an engine intake manifold to provide continual evacuation of gases from inside the crankcase in order to reduce degradation of various engine components in the crankcase. Crankcase ventilation systems may be intermittently monitored to identify breaches in the system. For example, a crankcase vent tube may become disconnected, an oil cap may be off or loose, a dipstick may be out, and/or other seals in the crankcase ventilation system may become broken resulting in degradation of various components included in the crankcase.
Diagnostic blow-by approaches may be used to monitor crankcase ventilation system integrity. For example, a pressure sensor may be used in the crankcase and a valve in a PCV fresh air hose may be opened so that pressure or vacuum changes may be sensed in the crankcase to determine if there is a breach in the system. In other approaches, a plurality of absolute sensors, e.g., a barometric pressure sensor (BP), a compressor inlet pressure sensor (CIP), a throttle inlet pressure sensor (TIP), a manifold air pressure sensor (MAP), etc., may be used in combination to monitor crankcase ventilation system integrity.
However, the inventors herein have recognized that such approaches may add additional hardware to such monitoring systems, e.g., additional sensors and valves, thus increasing costs and complexity of a crankcase ventilation monitoring system. In addition, based on the location of the sensor, some combinations of pressure sensors may read substantially the same pressure under certain conditions. As a result, system redundancy occurs without any improvement in the accuracy of a diagnostic routine.
In one approach, to at least partially address these issues, a method for an engine is provided. The method comprises indicating crankcase ventilation system degradation based on characteristics of a transient dip in crankcase vent tube pressure, during engine cranking. In this way, a system breach can be detected by an existing pressure sensor.
In one example, an engine crankcase ventilation system may include a crankcase vent tube coupled between an air intake passage and a crankcase. A pressure sensor (or flow sensor) may be positioned within the crankcase vent tube for providing an estimate of flow or pressure of air flowing through the vent tube. During engine cranking, and while an air flow through the vent tube and into the intake manifold is low, a transient dip in pressure may be sensed by the crankcase vent tube pressure sensor. In response to an amplitude of the transient dip being smaller than a threshold (e.g., a substantially negligible transient dip in crankcase vent tube pressure), a controller may infer that flow through the vent tube is disrupted due to a breach in the integrity of the crankcase ventilation system. For example, the controller may infer that the crankcase vent tube may have gotten disconnected.
The controller may further confirm crankcase system degradation based on a change in steady-state vent tube pressure relative to a change in steady-state manifold vacuum after engine cranking, and while manifold vacuum is higher than a threshold. For example, in response to the change in steady-state vent tube pressure not being varying with the change in steady-state manifold vacuum, crankcase system degradation may be determined and a mitigating action may be performed. This may include the controller setting an appropriate diagnostic code while also limiting engine speed or load so as to delay depletion of lubricant from the breached crankcase and aspiration of lubricant from the crankcase into engine components.
In this way, by using an existing pressure sensor to identify crankcase system breach, the number of sensors and valves employed in a crankcase ventilation monitoring system may be reduced, providing cost and complexity reduction benefits without reducing accuracy of degradation detection. By using different characteristics of a crankcase vent tube pressure sensor output during cranking as well as after cranking to detect crankcase system degradation, disconnection of a crankcase vent tube may be diagnosed more reliably and accurately. Further, the approach enables the crankcase ventilation system to remain active during a diagnostic procedure.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.